The present invention relates to a rotary processing apparatus for carrying out a predetermined process on a substrate to be processed, while rotating the substrate by means of a rotary table.
In a so-called photolithographic step of, for example, a semiconductor manufacturing process, a substrate to be processed, such as a semiconductor wafer (to be called wafer hereinafter) is cleaned, and a photoresist solution is applied on the surface of the wafer, thus forming a photoresist film on the substrate. Further, the photoresist film is exposed with a predetermined pattern, and then developed with a developer solution. For carrying out such a series of processing steps, a rotary processing apparatus is conventionally employed so as to carry out a predetermined process on a wafer while rotating the wafer by means of the rotary table.
In the case of such a rotary processing apparatus where a wafer is rotated on the rotary table driven by a motor serving as a rotary drive source, it is essential that the wafer is held firmly on the rotary table and rotated together with the rotary table. Therefore, a mechanical holding mechanism called, for example, mechanical chuck is conventionally used. The conventional mechanical holding mechanism holds a wafer by holding the outer periphery of the wafer from an outer side with a clamp member such as nail or ring. In the case of the conventional holding mechanism, the necessary holding force is obtained by utilizing the centrifugal force generated, for example, by the rotation of the rotary table.
However, in the conventional technique, if the rotation speed of the rotary table does not reach a certain degree, a holding force sufficient to hold a wafer cannot be obtained. For example, immediately after the start of the rotation of the rotary table, the rotary table has not yet been rotated at a sufficient rotational speed, and thus a necessary centrifugal force cannot be obtained. As a result, the positional displacement of the wafer easily occurs on the rotary table. Further, immediately before the rotation of the rotary table stops, the rotation speed of the table is lower than the predetermined degree, the positional displacement of the wafer easily occurs as well.